Chapter 4 Rocks
Section 1
rocks and rock cycle
• most rocks are made of common, rock forming minerals, like quartz, mica,
feldspar or calcite
• A rock is a mixture of minerals, volcanic glass, organic matter and other material
The rock cycle
• the rock cycle diagram shows how rocks change over time
• Rocks change from one type of rock to another by melting and cooling,
weathering and erosion, compaction and cementation and heat and pressure
Matter and the rock cycle
• Rocks can be broken down, changed or moved around, but never created or
destroyed
Discovering the rock cycle
 In 1788, scientist James Hutton recognized that rocks change over time, and
published his ideas
Section 2
Igneous rocks
• When hot magma and lava cool they form igneous rock
• Magma is molten rock beneath the earth’s surface, and has temps. Between 6501,200 Celsius
• Magma is less dense than surrounding rock, and is forced to the surface where it
becomes lava
Intrusive rocks
• Magma is made of melted minerals
• When magma cools slowly below the surface we call them intrusive igneous
rocks. These rocks are rough with large crystals
Extrusive rocks
• When lava on the surface cools quickly, we get extrusive igneous rocks that are
smoother with fine crystals that you can’t see
Volcanic glass
• Pumice, obsidian and scoria are examples
• These rocks cooled quickly, and scoria and pumice have holes from trapped gases
Classifying igneous rocks
• Are either intrusive or extrusive
• Igneous rocks form from basaltic, andesitic or granitic magma – b.a.g. of magma
• Basaltic magma – dark colored, low in silica, fluid like, gentle eruptions
• Granitic magma – light colored, high in silica, thick, explosive eruptions
• Andesitic magma – color is between basaltic and granitic, explosive
Section 3
Metamorphic rocks
• Rocks that have changed because of heat and pressure or hot, watery fluids
• The rock can change form, composition or both
Heat and pressure
• Deep in the earth minerals can be melted or flattened under the heat and pressure
• Depending on the amount of pressure and temp., one rock can change into other
rocks over time
– For example, shale changes to slate then phyllite then schist and then
gneiss
Hot fluids
 Water with dissolved elements moves through rocks and change their composition
Classifying metamorphic rocks
• They can be foliated, having minerals that line up in layers, like slate
• They can be non-foliated, where the minerals don’t line up, so they have no
layers, like marble
Section 4
Sedimentary rocks

Sedimentary rocks form when sediments are pressed and cemented together, or
when minerals come out of solution
Stacked rocks
• Sedimentary rocks that form in layers with the oldest layers on the bottom are
called stacked rocks
• Forces within the earth can sometimes turn over rock layers and change the order
Classifying sedimentary rocks
• Sedimentary rocks are made of pieces of all types of rock
• They are classified as either detrital, chemical or organic sedimentary rocks
Detrital sed. rocks
• Made of fragments of other rocks that are weathered and eroded mechanically and
chemically
• naturally compacted and cemented together
• Detrital rocks are named according to the size of their sediments
Chemical sed. rocks
• These form when dissolved minerals come out of solution
• Halite and limestone come out of salt water
Organic sed. rocks
• These are made from remains of once living things
• Coal forms from ancient plants
• Chalk comes from crushed shells